Method and an arrangement for initiating radiation absorption measurements of gaseous media

Abstract

The invention relates to an arrangement in an apparatus for analyzing, on the basis of radiation absorption properties, one or more gas component included in a gaseous medium from an origin, like exhaled air from a person. The apparatus comprises a radiation source ( 10 ); a measuring chamber ( 8 ) provided with radiation transmissive windows ( 7 a, 7 b ) for receiving a gas mixture ( 6 ) from at least the gaseous medium (G 1 ); a first detector ( 1 ), which receives the radiation passed through the gas mixture; and between the radiation source and the detector a first optical interference filter ( 3 ), which has a first radiation transmission wavelength band and which is tiltable (P) relative to the passing radiation (R) beam. The arrangement further comprises a second detector ( 2 ) directed towards a radiation input surface ( 5 b ) of the first interference filter, said second detector receiving momentarily a portion of said radiation (R) as reflected from said radiation input surface ( 5 b ) of the first interference filter ( 3 ) during the tilt (P) movement.

What is claimed is:  
     
       1. An apparatus for analyzing a gas mixture for one or more gas components that may be present in the gas mixture, the analysis of the one or more gas components being carried out on the basis of radiation absorption properties, said apparatus comprising: 
       a radiation source for providing a radiation beam;  
       a measuring chamber ( 6 ) for receiving a gas mixture, said measuring chamber having at least one radiation transmissive window ( 7   a,   7   b ) for the radiation of said radiation source, radiation from said radiation source passing through the gas mixture in said measuring chamber;  
       a first detector ( 1 ) for receiving radiation that has passed through said measuring chamber;  
       a first optical interference band pass filter ( 3 ) interposed in front of said detector along a path of said radiation beam, said first filter having a surface to which is applied radiation that has passed through said measuring chamber, said first filter having a radiation wavelength transmission band (λ 1 ) for transmitting radiation of the transmission band wavelength through the filter to said first detector, said surface reflecting radiation having wavelengths outside said radiation wavelength transmission band, said first filter being movable to a plurality of positions inclined with respect to the radiation beam for altering said radiation wavelength transmission band of said first filter, movement of said first filter causing movement of the radiation reflected from said surface; and  
       a second detector ( 2 ) positioned with respect to said first filter for receiving radiation reflected from said surface when said first filter is moved to a given one of said plurality of positions of said first filter.  
     
     
       2. An apparatus according to  claim 1  further including means coupled to said first detector for analyzing a gas component of the gas mixture on the basis of radiation received by said first detector when said first filter is in a plurality of positions. 
     
     
       3. An apparatus according to  claim 2  further including comparison means coupled to said first and second detectors for establishing a relationship between the transmitted radiation received by said first detector and the reflected radiation received by said second detector at said given one of said plurality of positions of said first filter. 
     
     
       4. An apparatus according to  claim 3  wherein said measuring chamber is further defined as receiving a reference gas mixture, and wherein said comparison means is further defined as establishing said relation for transmitted and reflected radiation when the reference gas mixture is in said measuring chamber for determining a characteristic of the reference gas mixture. 
     
     
       5. An apparatus according to  claim 4  wherein said reference gas mixture is ambient air, and wherein said gas mixture is the respiratory air of a person. 
     
     
       6. An apparatus according to  claim 1  further including comparison means coupled to said first and second detectors for establishing a relationship between the transmitted radiation received by said first detector and the reflected radiation received by said second detector at said given one of said plurality of positions of said first filter. 
     
     
       7. An apparatus according to  claim 6  wherein said measuring chamber is further defined as receiving a reference gas mixture, and wherein said comparison means is further defined as establishing said relationship for transmitted and reflected radiation when the reference gas mixture is in said measuring chamber for determining a characteristic of the reference gas mixture. 
     
     
       8. An apparatus according to  claim 7  further comprising selection means for providing the gas mixture to be analyzed or the reference gas mixture to said measuring chamber. 
     
     
       9. An apparatus according to  claim 1  wherein said radiation wavelength transmission band of said first filter is in the infrared region of radiation. 
     
     
       10. An apparatus according to  claim 9  wherein said radiation wavelength transmission band of said first filter includes a wavelength range of an absorption peak of a gas mixture gas component to be analyzed. 
     
     
       11. An apparatus according to  claim 1  further comprising a second optical interference band pass filter interposed in one of said radiation beam and reflected radiation, at least when said first filter is in said given one of said plurality of positions. 
     
     
       12. An apparatus according to  claim 11  wherein said second filter is positioned between said surface of said first filter and said second detector. 
     
     
       13. An apparatus according to  claim 11  wherein said second filter has a second radiation wavelength transmission band (λ 2 ) deviating from the absorption peak of gas components to be analyzed. 
     
     
       14. An apparatus according to  claim 11  wherein said radiation wavelength transmission bands of said first and second filters are in the infrared region of radiation. 
     
     
       15. An apparatus according to  claim 11  wherein said apparatus is further defined as one for analyzing an alcohol component that may be present in the respiratory air of a person and wherein said radiation wavelength transmission band (λ 1 ) of said first filter is in a range of 10 μm and wherein said radiation wavelength transmission band (λ 2 ) of said second filter is in a range of 10.6 μm and has a bandwidth of ±50 nm at maximum. 
     
     
       16. An apparatus according to  claim 11  wherein said arrangement is further defined as one for analyzing an alcohol component that may be present in the respiratory air of a person and wherein said radiation wavelength transmission band (λ 1 ) of said first filter is in a range of 3.5 μm and wherein said radiation wavelength transmission band of said second filter is in a range of 3.7 μm and has a bandwidth of ±50 nm at maximum. 
     
     
       17. A apparatus according to  claim 1  wherein said second detector is positioned such that an angle between the path of the radiation beam applied to said surface of said first filter and a path of the reflectived radiation received by said second detector when said first filter is moved to said given one of said plurality of positions of said first filter is within an angular range of 20° to 140°. 
     
     
       18. An apparatus according to  claim 17  wherein said angle is within an angular range of 40° to 70°. 
     
     
       19. An apparatus according to  claim 1  further comprising moving means for moving said first filter to a plurality of inclined positions, including a position in which specular reflection of radiation to said second detector occurs. 
     
     
       20. An apparatus according to  claim 19  wherein said moving means moves said first filter to a predetermined number of inclined positions for altering said wavelength transmission band of said first filter, and wherein said moving means maintains said first filter in each of said inclined positions for a predetermined period of time. 
     
     
       21. An apparatus according to  claim 20 , wherein said moving means maintains said first filter in an inclined position for a period up to 300 ms. 
     
     
       22. An apparatus according to  claim 21  wherein said moving means maintains said first filter in an inclined position for a period between 50 ms and 150 ms. 
     
     
       23. An apparatus according to  claim 19  wherein said moving means is further defined as establishing a number of inclined positions as a function of the number of gas components to be analyzed in the gas mixture. 
     
     
       24. An arrangement according to  claim 1  further defined as one for analyzing the respiratory air of a person. 
     
     
       25. An apparatus according to  claim 1  further including position calculating means ( 22 ) coupled to said second detector ( 2 ) for determining, from the reflected radiation, the inclined positions of said first filter and the relationship between the inclined positions and the alteration of said radiation wavelength transmission band. 
     
     
       26. An apparatus for analyzing the breathing gases of a person for alcohol, the analysis being carried out on the basis of infra red radiation absorption properties, said apparatus comprising: 
       a radiation source for providing an infra red radiation beam;  
       a measuring chamber ( 6 ) for selectively receiving the breathing gases of a person or ambient air, said measuring chamber having at least one radiation transmissive window ( 7   a,   7   b ) for the radiation of said radiation source, radiation from said radiation source passing through the contents of said measuring chamber;  
       a first detector ( 1 ) for receiving radiation that has passed through said measuring chamber;  
       a first optical interference band pass filter ( 3 ) interposed in front of said detector along a path of said radiation beam, said first filter having a surface to which is applied radiation that has passed through said measuring chamber, said first filter having a radiation wavelength transmission band (λ 1 ) for transmitting radiation of the transmission band wavelength through the filter to said first detector, said surface reflecting radiation having wavelengths outside said radiation wavelength transmission band, said first filter being movable to a plurality of positions inclined with respect to the radiation beam for altering said radiation wavelength transmission band of said first filter, movement of said first filter causing movement of the radiation reflected from said surface;  
       a second detector ( 2 ) positioned with respect to said first filter for receiving radiation reflected from said surface when said first filter is moved to a given one of said plurality of positions of said first filter;  
       means coupled to said first detector for analyzing the breathing gases for alcohol on the basis of radiation received by said first detector when said first filter is in a plurality of positions; and  
       comparison means coupled to said first and second detectors for establishing a relationship between the transmitted radiation received by said first detector and the reflected radiation received by said second detector at said given one of said plurality of positions of said first filter when ambient air is in said measuring chamber for determining the suitability of ambient air as a reference gas mixture.  
     
     
       27. A method for analyzing a gas mixture for one or more gas components that may be present in the gas mixture, the analysis of the one or more gas components being carried out on the basis of radiation absorption properties, said method comprising steps of: 
       providing a sample of a reference gas mixture;  
       passing a beam of radiation through the sample for absorption by the reference gas mixture;  
       applying the radiation passed through the reference gas mixture sample to a first optical interference bandpass filter, which has a first radiation wavelength transmission band;  
       placing the first filter in a given inclined position with respect to the beam of radiation;  
       allowing a portion of the radiation having wavelengths outside the first radiation wavelength transmission band to reflect from the first filter;  
       detecting an intensity of the radiation transmitted through the first filter and detecting an intensity of the radiation reflected from the first filter to determine a characteristic of the reference gas mixture;  
       providing a sample of the gas mixture to be analyzed;  
       passing the radiation through the gas mixture sample for absorption by the gas mixture to be analyzed;  
       applying the radiation passed through the gas mixture sample to be analyzed to the first filter;  
       moving the first filter to a plurality of inclined positions to provide wavelength shifting of the first radiation wavelength transmission band; and  
       detecting the intensity of the radiation passed through said gas mixture sample and transmitted through the first filter at the plurality of the inclined positions to analyze the one or more components of the gas mixture.  
     
     
       28. A method according to  claim 27  further comprising a step of applying the reflected radiation to a second optical interference filter having a second radiation wavelength transmission band. 
     
     
       29. A method according to  claim 28 , the method further comprising the steps of: 
       selecting the first radiation wavelength transmission band of the first filter so as to include an absorption peak of a gas mixture component which is to be analyzed; and  
       selecting the second radiation wavelength transmission band of the second optical interference filter deviating from the absorption peaks of the gas components to be analyzed.  
     
     
       30. A method according to  claim 29  further defined as one for analyzing the gas mixture for alcohol and wherein the first transmission band is selected to be in a range of 10 μm and the second transmission band is selected to be in a range of 10.6 μm. 
     
     
       31. A method according to  claim 30  further defined as analyzing the respiratory air of a person for alcohol. 
     
     
       32. A method according to  claim 29  further defined as one for analyzing a gas mixture for alcohol and wherein the first transmission band is selected to be in a range of 3.5 μm and the second transmission band is selected to be in a range of 3.7 μm. 
     
     
       33. A method according to  claim 21  further comprising, prior to providing a sample of the reference gas mixture, the steps of: 
       providing a sample of a calibrating gas mixture;  
       passing said radiation through the calibrating gas mixture; and  
       detecting an intensity of the radiation transmitted through the first filter and an intensity of the radiation reflected from the first filter at the given inclined position of the first filter.  
     
     
       34. A method according to  claim 33  further comprising the step of determining a first relationship between the transmitted radiation intensity and the reflected radiation intensity for the calibrating gas mixture sample. 
     
     
       35. A method according to  claim 34  further comprising the steps of: 
       determining a second relationship between the transmitted radiation intensity and the reflected radiation intensity for the reference gas mixture sample;  
       comparing the second relationship with the first relationship to determine a characteristic of the reference gas mixture; and  
       controlling the carrying out of the steps of the method in accordance with the comparison of the first relationship and the second relationship.  
     
     
       36. A method according to  claim 35  further defined as one for analyzing the respiratory air, of a person for alcohol and as allowing measuring for a concentration of alcohol in the respiratory air of the person if the difference between the first relationship and the second relationship is smaller than a predetermined value. 
     
     
       37. A method for analyzing a gas mixture for one or more gas components that may be present in the gas mixture, said process comprising the steps of: 
       providing a sample of the gas mixture;  
       passing a beam of radiation through the sample for absorption by the gas mixture;  
       applying the radiation passed through the gas mixture sample to a radiation input surface of a first optical interference bandpass filter which has a first radiation wavelength transmission band;  
       moving the first filter to a plurality of positions that are inclined with respect to the beam of radiation to provide a wavelength shifting of the first radiation wavelength transmission band;  
       allowing a portion of the radiation having wavelengths outside the first radiation wavelength transmission band to reflect from the radiation input surface;  
       detecting an inclined position of the first filter for which specular reflection of said radiation to a second detector directed towards the radiation input surface of the first optical interference filter occurs; and  
       calculating, for the inclined position of the first filter, a center wavelength of the first radiation wavelength transmission band.  
     
     
       38. A method according to  claim 37 , further comprising the step of calculating a connection between predetermined inclined positions, respective center wavelengths and effective wavelength distributions of the first radiation wavelength transmission band. 
     
     
       39. A method according to  claim 38 , further comprising, prior to providing the sample of said gas mixture, the steps of: 
       providing a sample of a reference gas mixture;  
       passing said radiation through the reference gas sample;  
       detecting an intensity of the radiation transmitted through the first filter and an intensity of the radiation reflected from the first filter at least one of inclined position of the first filter; and  
       determining a first relationship between the transmitted radiation intensity and the reflected radiation intensity indicative of a characteristic of the reference gas mixture.  
     
     
       40. A method according to  claim 39 , further comprising, prior to providing a sample of said reference gas mixture, the steps of: 
       providing a sample of a calibrating gas mixture;  
       passing said radiation through the calibrating gas sample;  
       detecting an intensity of the radiation transmitted through the first filter and an intensity of the radiation reflected from the first filter at least one inclined position of the first filter; and  
       determining a second relationship between said transmitted radiation intensity and said reflected radiation intensity.  
     
     
       41. A method according to  claim 40 , further comprising the steps of: 
       comparing said first relationship and said second relationship; and  
       controlling the carrying out of the steps of the method in accordance with the comparison of the first relationship and the second relationship.